The present invention relates generally to acoustic structures, and more particularly to sound barrier panels for eliminating or reducing noise emanating from roadways, railways, airports or other noise generating areas. Further the present invention is directed to sound barrier panels that are made from waste materials, including scrap carpet fibers, scrap fiberglass reinforced plastic (FRP) and recyclable plastics.
As new and existing residential areas and high volume highways continue to intermingle, sound barriers placed between highways and residential neighborhoods provide an effective way to control and limit the amount of traffic noise that reaches the residential neighborhoods.
In recent years, state highway commissions and transportation departments have promulgated noise level standards for highways passing through urban neighborhoods. Studies have established that exposure to highway noise can adversely impact the quality of people's lives. It has also been suggested that high decibel levels along highways may be linked to sleep disturbance, hearing loss, high blood pressure, irritability, ulcers, and heartburn, among other ailments.
The federal Environmental Protection Agency has determined that noise levels above 66 decibels are unsafe for residential areas, while 72 dB is the limit for commercial environments. As a reference for sound levels, a standard pickup truck at 50 mph produces noise at 70 dB, while a medium truck is twice as loud at 80 dB. A motorcycle can reach 90 dB, which is four times louder than the pickup truck (the decibel (dB) is a logarithmic unit).
Highway noise is not merely a function of the total sum noise of each individual vehicle. Sound sources include engine noise, tire noise, and aerodynamic noise, all of which vary by vehicle type and speed. For instance, highway noise doubles when the traffic increases from 200 vehicles per hour to 2000 vehicles per hour, or when traffic speed increases from 30 mph to 65 mph. A single semi-trailer truck at 55 mph produces as much noise as ten cars at the same speed.
Different approaches have been devised to address the problem of traffic noise. Some noise abatement systems involve designing the roads themselves to reduce vehicle noise. Lower highway speed limits within city limits can reduce noise. For new developments, buffer zones can be provided between the residential or commercial buildings and highways. On the other hand for many older neighborhoods, traffic volume has steadily increased over the years as the traffic flow on the adjacent roads has increased. For these neighborhoods, sound barriers are the most viable solution.
Effective noise abatement systems can reduce sound levels 10-15 dB, cutting the loudness of the traffic in half. Where space permits, earth barriers are relatively inexpensive and can be used to improve the ecological aesthetics of the neighborhood. This approach is common for new neighborhoods but not often available for existing residential areas. Walls, on the other hand, take up less space.
Sound barriers (also called noise barriers or acoustical barriers) reduce the sound which enters a community from a busy highway by absorbing the sound, reflecting the sound back across the highway, or forcing the sound to take a longer path over and/or around the barrier.
Sound barriers can be constructed from earth, concrete, masonry, wood, metal, and other materials. To effectively reduce sound transmission through the barrier, the material chosen must be rigid and sufficiently dense (at least 20 kilograms/square meter). All noise barrier material types are equally effective, acoustically, if they have sufficient density.
Noise barriers are required to have structural integrity, acoustic effectiveness and durability. In this regard concrete sound barrier walls are perhaps the most frequently used because they require only minimal continuing upkeep and are very weather resistant. Moreover, the ability to produce pre-fabricated concrete panels can simplify construction, while also providing the ability to add aesthetic features to the panels.
The present invention provides sound barriers that are made from recycled materials and which demonstrate desirable structural integrity, acoustic effectiveness and durability. Further the present invention effectively reduces sound transmission.
Most sound barriers in existence today are reflective sound barriers that do not absorb incident sound. Sound barriers that absorb incident sound reduce sound reflection in addition to reducing sound transmission. One embodiment of the present invention allows existing reflective sound barriers to be converted into sound absorbing sound barriers, further reducing overall noise levels.